US 6353507 B1 Abstract A zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object, and thereby zooming is performed by moving the first through third lens groups along the optical axis. The zoom lens system satisfies the following condition:
wherein
d
f
Claims(7) 1. A zoom lens system comprising a negative first lens group, a positive second lens group, and a negative third lens group, in this order from an object,
wherein zooming is performed by moving said first through third lens groups along the optical axis of said zoom lens system; and
wherein said zoom lens system satisfies the following condition:
_{12W}/f_{W}≦0.18 wherein
d
_{12W }designates the distance between said first lens group and said second lens group at the short focal length extremity; and f
_{W }designates the focal length of the entire lens system at the short focal length extremity. 2. The zoom lens system according to
3Gwherein
f
3G f
3. A zoom lens system comprising a negative first lens group, a positive second lens group, and a negative third lens group, in this order from an object,
wherein zooming is performed by moving said first through third lens groups along the optical axis of said zoom lens system; and
wherein said zoom lens system satisfies the following conditions:
_{12W}/f_{W}<0.35 _{10}Z_{12}/log_{10}Z<0.15 wherein
d
_{12W }designates the distance between said first lens group and said second lens group at the short focal length extremity; f
_{W }designates the focal length of the entire lens system at the short focal length extremity; _{12}=f_{12T}/f_{12W}; _{T}/f_{W}; f
_{12T }designates the resultant focal length of said first lens group and said second lens group at the long focal length extremity; f
_{12W }designates the resultant focal length of said first lens group and said second lens group at the short focal length extremity; and f
_{T }designates the focal length of the entire lens system at the long focal length extremity. 4. The zoom lens system according to
_{T}/|f_{3G}|<8 wherein
f
_{3G }designates the focal length of said third lens group; and f
_{T }designates the focal length of the entire lens system at the long focal length extremity. 5. A zoom lens system comprising a negative first lens group, a positive second lens group, and a negative third lens group, in this order from an object,
wherein zooming is performed by moving said first through third lens groups along the optical axis of said zoom lens system; and
wherein said zoom lens system satisfies the following conditions:
_{12W}/f_{W}<0.35 _{T}/f_{12T}<6 wherein
d
_{12W }designates the distance between said first lens group and said second lens group at the short focal length extremity; f
_{W }designates the focal length of the entire lens system at the short focal length extremity; f
_{T }designates the focal length of the entire lens system at the long focal length extremity; and f
_{12T }designates the resultant focal length of said first lens group and said second lens group at the long focal length extremity. 6. The zoom lens system according to
_{T}/|f_{3G}|<8 wherein
f
_{3G }designates the focal length of said third lens group; and f
_{T }designates the focal length of the entire lens system at the long focal length extremity. 7. A zoom lens system consisting essentially of, in order from an object, a negative first lens group, a positive second lens group, and a negative third lens group which are moved with respect to one another during zooming,
wherein said zoom lens system satisfies the following conditions:
_{12W}/f_{W}<0.35 _{T}/|f_{3G}|<8 wherein
d
_{12W }designates the distance between said first lens group and said second lens group at the short focal length extremity; and f
_{W }designates the focal length of the entire lens system at the short focal length extremity f
_{3G }designates the focal length of said third lens group; and f
_{T }designates the focal length of the entire lens system at the long focal length extremity. Description 1. Field of the Invention The present invention relates to a zoom lens system for a compact camera, and in particular, relates to achieving a high zoom ratio, and achieving miniaturization of the zoom lens system. 2. Description of the Related Art In a zoom lens system for a compact camera, there is no need to provide a long back focal distance, unlike a zoom lens system for a single lens reflex (SLR) camera which requires a space for providing a mirror behind the photographing lens system. Accordingly, a compact camera generally employs a telephoto-type lens system in which positive and negative lens groups are provided in this order from the object, while a SLR camera generally employs a retrofocus type lens system in which negative and positive lens groups are provided in this order from the object. In recent years, there have been increasing demands for further miniaturization and a higher zoom ratio in zoom lens systems for compact cameras. In order to satisfy the demands for miniaturization, it is preferable to employ a two-lens-group zoom lens system having a small number of lens elements. However, if an attempt is made to obtain a zoom ratio of more than 3.5, a three-lens-group zoom lens system has to be used because a two-lens-group zoom lens system has a limit in obtaining well-balanced aberrations at focal length points in a range determined by the short focal length extremity and the long focal length extremity. However, a conventional three-lens-group zoom lens system is not suitable for miniaturization, since the overall length is longer, and the diameter of the front lens group is larger, compared with a two-lens-group zoom lens system. It is an object of the present invention to provide a three-lens-group zoom lens system of a telephoto type, which attains a zoom ratio (i.e., the focal length at the long focal length extremity/the focal length at the short focal length extremity) of about 3.5 to 4 and whose overall length and diameter of the most object-side lens element are short and small enough to the extent that the same are equivalent to those of a two-lens-group zoom lens system. In order to achieve the above mentioned object, there is provided a zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order form the object, and whereby zooming is performed by moving the first through third lens groups along the optical axis. Further, the zoom lens system satisfies the following condition:
wherein d f The zoom lens system preferably satisfies the following condition:
wherein Z Z=f f f f The zoom lens system preferably satisfies the following condition:
wherein f f The zoom lens system preferably satisfies the following condition:
wherein f The present disclosure relates to subject matter contained in Japanese patent Application No. Hei-10-368173 (filed on Dec. 24, 1998) which is expressly incorporated herein in its entirety. The invention will be discussed below in detail with reference to the accompanying drawings, in which: FIG. 1 is a lens arrangement of a first embodiment of a zoom lens system according to the present invention; FIGS. 2A, FIGS. 3A, FIGS. 4A, FIG. 5 is a lens arrangement of a second embodiment of a zoom lens system according to the present invention; FIGS. 6A, FIGS. 7A, FIGS. 8A, FIG. 9 is a lens arrangement of a third embodiment of a zoom lens system according to the present invention; FIGS. 10A, FIGS. 11A, FIGS. 12A, FIG. 13 is a lens arrangement of a fourth embodiment of a zoom lens system according to the present invention; FIGS. 14A, FIGS. 15A, FIGS. 16A, FIG. 17 is the lens-group moving paths of a zoom lens system according to the first embodiment; FIG. 18 is the lens-group moving paths of a zoom lens system according to the second and fourth embodiments; and FIG. 19 is the lens-group moving paths of a zoom lens system according to the third embodiment. As shown in the lens group moving paths of FIGS. 17 Condition (1) specifies the distance between the negative first lens group If d If d Condition (2) specifies the resultant focal length of the first lens group If log If log In a three-lens-group zoom lens system, where the first lens group Condition (3) specifies the resultant focal length of the negative first lens group If f If f Condition (4) specifies the focal length of the negative third lens group If f If f Specific numerical examples will herein be discussed. In the diagrams of chromatic aberration (axial chromatic aberration) represented by spherical aberration, the solid lines and the two types of dotted lines respectively indicate spherical aberration with respect to the d, g and C lines. Also, in the diagrams of lateral chromatic aberration, the solid lines and the two types of dotted lines respectively indicate magnification with respect to the d, g and C lines. S designates the sagittal image, and M designates the meridional image. In the tables, F In addition to the above, an aspherical surface which is symmetrical with respect to the optical axis is defined as follows: x=Ch wherein: x designates a distance from a tangent plane of an aspherical vertex; C designates a curvature of the aspherical vertex (1/R); h designates a distance from the optical axis; K designates the conic coefficient; A4 designates a fourth-order aspherical coefficient; A6 designates a sixth-order aspherical coefficient; A8 designates a eighth-order aspherical coefficient; and A10 designates a tenth-order aspherical coefficient; FIG. 1 is a lens arrangement of the first embodiment of the zoom lens system. FIGS. 2A through 2D, FIGS. 3A through 3D, and FIGS. 4A through 4D show aberration diagrams of the lens arrangement of FIG. 1 respectively at the short focal length extremity, an intermediate focal length, and the long focal length extremity. Table 1 shows the numerical data thereof. Surface Nos. 1 through 4 designate the negative first lens group
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
FIG. 5 is a lens arrangement of the second embodiment of the zoom lens system. FIGS. 6A through 6D, FIGS. 7A through 7D and FIGS. 8A through 8D show aberration diagrams of the lens arrangement of FIG. 5 respectively at the short focal length extremity, an intermediate focal length and the long focal length extremity. Table 2 shows the numerical data thereof. Surface Nos. 1 through 3 designate the negative first lens group
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
FIG. 9 is a lens arrangement of the third embodiment of the zoom lens system. FIGS. 10A through 10D, FIGS. 11A through 11D and FIGS. 12A through 12D show aberration diagrams of the lens arrangement of FIG. 9 respectively at the short focal length extremity, an intermediate focal length and the long focal length extremity. Table 3 shows the numerical data thereof. The basic lens arrangement is the same as the second embodiment. In FIG. 19, the lens group moving paths of the zoom lens system according to the third embodiment are shown.
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
FIG. 13 is a lens arrangement of the fourth embodiment of the zoom lens system. FIGS. 14A through 14D, FIGS. 15A through 15D and FIGS. 16A through 16D show aberration diagrams of the lens arrangement of FIG. 13 respectively at the short focal length extremity, an intermediate focal length and the long focal length extremity. Table 4 shows the numerical data thereof. The basic lens arrangement is the same as the second embodiment. In FIG. 18, the lens-group moving paths of the zoom lens system according to the fourth embodiment are shown.
Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
Table 5 shows the numerical values of each condition for each embodiment.
As can be understood from Table 5, each embodiment satisfies each condition, and as can be understood from the aberration diagrams, aberrations are adequately corrected. According to the above description, a three-lens-group zoom lens system of a telephoto type can attain a zoom ratio of about 3.5 to 4. Furthermore, in the three-lens-group zoom lens system of a telephoto type, the overall length and the diameter of the most object-side lens element are short and small enough to the extent that the same are equivalent to those of a two-lens-group zoom lens system. Patent Citations
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